An increasingly large number of automobiles are equipped with a passive restraint system which employs an inflatable air bag in case of a vehicle crash by detecting a large deceleration of the vehicle. Such an inflatable bag is normally installed inside a central part of a steering wheel for protecting the vehicle operator. To protect the vehicle occupant sitting next to the vehicle operator, an inflatable bag may be installed inside a part of the instrument panel opposing the vehicle occupant. To protect the vehicle occupants sitting in the rear seat, inflatable bags may be installed in the front seats or other suitable locations.
When a vehicle runs into an oncoming vehicle or a stationary object, a large deceleration acts upon the vehicle, and the vehicle occupant experiences an apparent force or an inertia force which pushes the vehicle occupant forward. A passive restraint system restrains the vehicle occupant from such a forward movement upon detecting a strong deceleration, and thereby prevents the vehicle occupant from hitting the windshield or other parts of the vehicle, and being thereby injured.
It is therefore essential for a passive restraint system using an inflatable air bag to be able to deploy the air bag in a short time period after detecting a large deceleration. For the air bag to be able to quickly deploy itself, the air bag must be free from leakage so that the gas for inflating the air bag may be fully utilized. Also, to fully utilize the energy of the gas for inflating the air bag, the air bag must inflate toward the vehicle occupant without excessively bulging in lateral directions.
Normally, an air bag is made of nylon fabric coated with rubber, and its open base end is connected to a housing for an inflator or a gas producing unit.
The air bag is normally folded, and received in an air bag housing. Upon detecting a strong deceleration, the inflator produces gas, and inflates the air bag. Because the production of the gas occurs in an almost explosive fashion so that the air bag may be deployed in a short time, gas pressure builds up extremely suddenly in the region near the open base end of the air bag, and an effective sealing arrangement is necessary in the open end of the air bag. Therefore, there has been a demand for a simple and economical structure which can firmly secure the open end of an air bag, and eliminate the possibility of gas leakage.
Because of the need to be stowed in a relatively small compartment provided inside an instrument panel or the like, an air bag system is desired to be as compact as possible. On the other hand, the housing for the air bag should not hinder the deployment of the air bag. Furthermore, if the air bag housing has an insufficient rigidity, when the air bag is inflated, the housing may be deformed, and may allow the air bag to be inflated laterally. This reduces the impetus of the air bag to be properly deployed, and is therefore undesirable. Conversely, if the housing is too rigid, it will present a rigid surface in front of a vehicle, occupant, and the capability of the area accommodating the air bag to absorb impact is reduced. This is not desirable because additional padding may be necessary to achieve a desired impact absorbing capability in this area.
The part of the instrument panel or the like in which an air bag system is installed is normally closed by a lid which can readily rupture when the air bag is deployed, and this lid may be mounted either on a housing accommodating the inflator for producing the gas and/or the air bag, or on the instrumental panel either directly or via a frame structure.
In the former case, there is some difficulty in aligning the lid with the opening provided in the instrument panel. In the latter case, the instrument panel is significantly damaged whenever the air bag is activated, and the repair subsequent to the deployment of the air bag is unacceptably costly.